Skin, the largest organ of the human body, has important functions in protecting the body from infection, toxins, microbes, and radiation. Although the type of skin varies over the body, skin generally has two main layers of tissue. The epidermis or cuticle, the outermost layer, is composed of three superficial and two deep cellular layers. The derma, corium, or cutis vera, the true skin, is composed of a papillary layer above and a reticular layer below. It contains blood vessels that nourish the skin cells and the structural elements e.g., collagen and elastin, which keep the skin firm and springy.
The epithelial cells of the skin are constantly dying and being replaced by new cells, to the extent that human skin renews its surface layers every three to four weeks. Unlike the epithelial cells, collagen cells in the subcutaneous layer of will not be replaced for around 30 years. When these old collagen cells breakdown due to aging, sun damage, smoking, poor hydration or steroid overuse, the fragmented collagen causes folds, ridges or creases in the skin, i.e., wrinkles. Fragmented collagen also leads to skin tearing and bruising easier than it otherwise would. Wrinkles are a reflection of slower skin regeneration. The color and appearance of the skin deteriorates slowly due to aging, exposure to sunlight and radiation, and/or degradation of the dermal-epidermal junction and of the cell-cell cohesion in the epidermis. Because the changes of skin appearance cause significantly psychological, social and occupational problems, there is an increasing demand in mitigating or delaying the dermatological signs of chronologically or photo-aged skin, such as fine lines, wrinkles, and sagging skin.